| Static cracking agent(SCA)is powdery substance that cracking bridle by generating volume expansion during hydration reaction and its main ingredient is calcium oxide.Static cracking technology is a technique that applies SCA to crack fragile material with synthesizing the technology of drilling hole,charging technology,hole sealing etc.As static cracking technology possesses the characteristics of safety and non-toxic,convenient transportation etc,nowadays,it has been widely applied to industry,agriculture and military areas.In this paper,the development status of static cracking technology at home and abroad had been summarized.Based on the analysis of the cracking mechanism and influence factors of SCA,the tests of mix ratio,volume expansion rate and expansion pressure about hydration reaction on SCA severally mixing with three difference kinds of solid hydrate — alum,gel and super absorbent polymer — had been carried out,and their reaction rate,volume expansion rate and expansion pressure were tested as well.When the mix proportion of solid hydrate and SCA is in the range of 0.27~0.42,the highest temperature range that SCA hydrate reaction can arrive is 150~170 ?.The arrival time range is 10~20minutes,and the smaller mix proportion leads to the faster reaction rate;The volume after the reaction turns into almost 3 times bigger than that before the reaction.The results of expansion pressure test show expansion pressure is considerably influenced by the solid hydrate species and the mixing ratio.When the mixing ratio is fixed and small,the expansion pressure of hydration reaction which super absorbent polymer and gel respectively took part in is higher than that alum did.When the mixing ratio is fixed and large,the result is opposite.When the solid hydrate is the same,the expansion pressure of hydration reaction which super absorbent polymer and gel respectively took part in will decrease with the increase of mix proportion.However,the expansion pressure of hydration reaction which alum took part in will increase with the increase of mix proportion.The SCA control test showed when the heating time range of the special AC electric heating resistance stick was from 300 s,600,900 s to heating during the whole process,the times that the expansion pressure of SCA reached its highestwere 54 min,41min,33 min and 30 min respectively.It indicates the longer heating time means the shorter time that the expansion pressure of SCA reached its highest and the higher cracking efficiency.Finally,the three groups of cracking effect contrast experiments had been designed.The results of contrast experiments between the conventional cracking method and the cracking method in this paper show:The concrete specimen began to crack after 9h in the conventional cracking way,and completely cracked after24 h,while the concrete specimen in the cracking method in this paper would never crack under no heating condition.The cracking contrast experiments of concrete specimens with 40 mm bore diameter and 60 mm bore diameter,50 mm bore diameter and 60 mm bore diameter showed:The time of 40 mm bore diameter,50 mm bore diameter and 60 mm bore diameter concrete specimens under heating condition from the beginning of the hydration reaction to the crack were 40 min,30min and 15 min respectively,and from the beginning of the cracks appearing to the crack extended no longer obviously were 15 mins,12mins and9 mins severally.This indicated that the larger bore diameter was,the earlier concrete specimen would crack,and the higher the cracking efficiency would be.The cracking time of concrete specimens in the cracking method in this paper from the moment hole was sealed to the moment the crack extended no longer obviously was only 5 hours,and the time of the whole cracking process is just 12 hours.Compared to the conventional cracking method,it greatly improved the cracking efficiency. |
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